Effects of tracheal intubation and tracheal tube position on regional lung ventilation: an observational study.

Anaesthesia and positive pressure ventilation cause ventral redistribution of regional ventilation, potentially caused by the tracheal tube. We used electrical impedance tomography to map regional ventilation during anaesthesia in 10 patients with and without a tracheal tube. We recorded impedance data in subjects who were awake, during bag-mask ventilation, with the tracheal tube positioned normally, rotated 90° to each side and advanced until in an endobronchial position. We recorded the following measurements: ventilation of the right lung (proportion, %); centre of ventilation (100% = entirely ventral); global inhomogeneity (0% = homogenous); and regional ventilation delay, an index of temporal heterogeneity. We compared the results using Student's t-tests. Relative to subjects who were awake, anaesthesia with bag-mask ventilation reduced right-sided ventilation by 5.6% (p = 0.002), reduced regional ventilation delay by 1.6% (p = 0.025), and moved the centre of ventilation ventrally from 51.4% to 58.2% (p = 0.0001). Tracheal tube ventilation caused a further centre of ventilation increase of 1.3% (p = 0.009). With the tube near the carina, right-sided ventilation increased by 3.2% (p = 0.031) and regional ventilation delay by 2.8% (p = 0.049). Tube rotation caused a 1.6% increase in right-sided ventilation compared with normal position (p = 0.043 left and p = 0.031 right). Global inhomogeneity remained mostly unchanged. Ventral ventilation with positive pressure ventilation occurred with bag-mask ventilation, but was exacerbated by a tracheal tube. Tube position influenced ventilation of the right and left lungs, while ventilation overall remained homogenous. Tube rotation in either direction resulted in ventilation patterns being closer to when awake than either bag-mask ventilation or a normally positioned tube. These results suggest that even ideal tube positioning cannot avoid the ventral shift in ventilation.

Pre-operative respiratory optimisation: an expert review.

Postoperative pulmonary complications are common and cause increased mortality and hospital stay. Smoking and respiratory diseases including asthma, chronic obstructive pulmonary disease and obstructive sleep apnoea are associated with developing postoperative pulmonary complications. Independent risk factors for such complications also include low pre-operative oxygen saturation, or a recent respiratory infection. Postponing surgery in patients who have respiratory infections or inadequately treated respiratory disease, until these can be fully treated, should, therefore, reduce postoperative pulmonary complications. There is evidence from several studies that pre-operative smoking cessation reduces such complications, with no agreed duration at which the benefits become significant; the longer the abstinence, the greater the benefit. Intensive smoking cessation programmes are more effective, and there are long-term benefits, as many patients become permanent non-smokers following their surgery. Supervised exercise programmes normally last 6-8 weeks, and although they reduce overall complications, the evidence of benefit for postoperative pulmonary complications is mixed. High-intensity interval training can improve fitness in just 2 weeks, and so may be more useful for surgical patients. Specific respiratory pre-operative interventions, such as deep breathing exercises and incentive spirometry, can help when used as components of a package of respiratory care. Pre-operative inspiratory muscle training programmes that involve inspiration against a predetermined respiratory load may also reduce some postoperative pulmonary complications. Pre-operative exercise programmes are recommended for patients having major surgery, or in those where pre-operative testing has shown low levels of cardiorespiratory fitness; interval training or respiratory interventions are more feasible as these reduce complications after a shorter pre-operative intervention.

Erratum to 'Pulmonary function tests in anaesthetic practice' [BJA Educ 19 (2019) 206-211].

[This corrects the article DOI: 10.1016/j.bjae.2019.02.001.].

Postoperative pulmonary complications.

Postoperative pulmonary complications (PPCs) are common, costly, and increase patient mortality. Changes to the respiratory system occur immediately on induction of general anaesthesia: respiratory drive and muscle function are altered, lung volumes reduced, and atelectasis develops in > 75% of patients receiving a neuromuscular blocking drug. The respiratory system may take 6 weeks to return to its preoperative state after general anaesthesia for major surgery. Risk factors for PPC development are numerous, and clinicians should be aware of non-modifiable and modifiable factors in order to recognize those at risk and optimize their care. Many validated risk prediction models are described. These have been useful for improving our understanding of PPC development, but there remains inadequate consensus for them to be useful clinically. Preventative measures include preoperative optimization of co-morbidities, smoking cessation, and correction of anaemia, in addition to intraoperative protective ventilation strategies and appropriate management of neuromuscular blocking drugs. Protective ventilation includes low tidal volumes, which must be calculated according to the patient's ideal body weight. Further evidence for the most beneficial level of PEEP is required, and on-going randomized trials will hopefully provide more information. When PEEP is used, it may be useful to precede this with a recruitment manoeuvre if atelectasis is suspected. For high-risk patients, surgical time should be minimized. After surgery, nasogastric tubes should be avoided and analgesia optimized. A postoperative mobilization, chest physiotherapy, and oral hygiene bundle reduces PPCs.

Computational fluid dynamic modelling of the effect of ventilation mode and tracheal tube position on air flow in the large airways.

We have used computational fluid dynamic modelling to study the effects of tracheal tube size and position on regional gas flow in the large airways. Using a three-dimensional mathematical model, we simulated flow with and without a tracheal tube, replicating both physiological and artificial breathing. Ventilation through a tracheal tube increased proportional flow to the left lung from 39.5% with no tube to 43.1-47.2%, depending on tube position. Ventilation mode and tube distance from the carina had no effect on flow. Lateral displacement and deflection of the tube increased ventilation to the ipsilateral lung; for example, when deflected 10° to the left of centre, flow to the left lung increased from 43.8 to 53.7%. Because of the small diameter of a tracheal tube relative to the trachea, gas exits a tube at high velocity such that regional ventilation may be affected by changes in the position and angle of the tube.

The effect of coughing at extubation on oxygenation in the post-anaesthesia care unit.

We prospectively studied 84 patients to investigate whether there is a relationship between coughing during emergence and tracheal extubation, and impaired oxygenation in the post-anaesthesia care unit. Our primary outcome measure was a change in the alveolar-arterial oxygen partial pressure gradient ((A-a)DO2 ) between time A (during general anaesthesia) and time B (1 h after extubation). Patients demonstrated a worsening of oxygenation with mean (SD) (A-a)DO2 increasing from 7.5 (5.2) kPa at time A to 13.9 (4.2) kPa at time B (p < 0.01). An overall linear regression model was not predictive for the observed change (adjusted R(2) = 0.01, p = 0.31) and nor were any of the individual predictors studied, including subjective cough score (p = 0.33), number of coughs (p = 0.95) and duration of coughing (p = 0.39). Despite the abnormal cough that occurs while tracheally intubated, we have been unable to demonstrate that coughing at extubation is associated with impaired oxygenation in the immediate postoperative period.

Lung recruitment and positive airway pressure before extubation does not improve oxygenation in the post-anaesthesia care unit: a randomized clinical trial.

BACKGROUND: Atelectasis is known to develop during anaesthesia and after operation atelectasis leads to impaired oxygenation. Lung recruitment manoeuvres, positive end-expiratory pressure (PEEP), and continuous positive airway pressure (CPAP) have been proposed for reduction of atelectasis but their benefits have not been shown to persist after operation. We proposed that a combination of these techniques before extubation would improve oxygenation after operation. METHODS: Adult patients undergoing elective surgery requiring tracheal intubation and an arterial catheter were randomized to receive either: a lung recruitment manoeuvre of 40 cm H(2)O for 15 s, 30 min before the end of anaesthesia, followed by 10 cm H(2)O of PEEP and then 10 cm H(2)O of CPAP from return of spontaneous breathing until extubation; or no lung recruitment manoeuvre,

New aspects of ventilation in acute lung injury.

Recent recognition that artificial ventilation may cause damage to the acutely injured lung has caused renewed interest in ventilation techniques that minimise this potential harm. Many ventilation techniques have proved beneficial in small trials of very specific patient groups, but most have subsequently failed to translate into improved patient outcome in larger trials. An exception to this is 'protective ventilation' using reduced tidal volumes (to lower airway pressure) and increased PEEP (to reduce pulmonary collapse). Results of trials of protective ventilation have been encouraging, and the technique should now be adopted more widely. High frequency ventilation, inverse ratio ventilation, prone positioning and inhaled nitric oxide are all techniques that may be considered when, in spite of optimal artificial ventilation, the patient's gas exchange remains dangerously poor. Under these circumstances, the choice of technique is dependent on their availability, local expertise and individual patient needs.